Liquid Crystal Display Device and Method for Driving Same

1. A liquid crystal display device that applies a voltage corresponding to input image data to a liquid crystal layer of a display unit, and displays an image represented by the input image data on the display unit, the liquid crystal display device comprising: a drive unit configured to apply the voltage corresponding to the input image data to the liquid crystal layer; and a display control unit configured to generate an alternating current voltage upon receiving an off signal that stops at least a part of functions of the liquid crystal display device, and to control the drive unit to apply the alternating current voltage to the liquid crystal layer, wherein the display unit includes a plurality of pixel formation portions configured to hold, as a data voltage, the voltage to be applied to the liquid crystal layer, the display control unit includes: a polarity bias calculation unit configured to obtain a polarity bias value of the voltage applied to the liquid crystal layer; an alternating current voltage generation unit configured to generate the alternating current voltage upon receiving the off signal; and a balance control unit configured to control the drive unit so that an operation of the drive unit is different before and after a point of time when the off signal is inputted, and after the point of time when the off signal is inputted when the polarity bias value at the point of time when the off signal is inputted is larger than “0”, the polarity bias value being obtained by the polarity bias calculation unit, the balance control unit controls the drive unit to apply, to each of the plurality of pixel formation portions, the alternating current voltage generated in the alternating current voltage generation unit.

2. The liquid crystal display device according to claim 1 , wherein the display control unit further includes a REF/NREF determination unit configured to determine, for each frame period, whether the frame period is a refresh period of writing the data voltage into the plurality of pixel formation portions or a pause period of pausing the write of the data voltage into the plurality of pixel formation portions, and the polarity bias calculation unit holds the polarity bias value obtained based on a result of the determination by the REF/NREF determination unit, and outputs, to the balance control unit, the polarity bias value at the point of time when the off signal is inputted.

3. The liquid crystal display device according to claim 2 , wherein, before the point of time when the off signal is inputted, the balance control unit controls the drive unit so that the refresh period of writing the data voltage into the plurality of pixel formation portions and the pause period of pausing the write of the data voltage into the plurality of pixel formation portions appear alternately based on the result of the determination by the REF/NREF determination unit.

4. The liquid crystal display device according to claim 1 , further comprising: a plurality of data signal lines and a plurality of scanning signal lines, both of which are formed in the display unit and configured to connect the pixel formation portions and the drive unit, wherein the balance control unit controls the drive unit to sequentially activate the plurality of scanning signal lines collectively every one or more lines, and to apply the alternating current voltage to the plurality of data signal lines.

5. The liquid crystal display device according to claim 4 , further comprising: a backlight unit provided on a back surface side of the display unit and configured to radiate backlight toward the display unit, wherein the balance control unit controls the backlight unit to turn off a power supply of the backlight unit when the alternating current voltage is applied to the pixel formation portions.

6. The liquid crystal display device according to claim 1 , further comprising: data signal lines and scanning signal lines, both of which are formed in the display unit and are configured to connect the pixel formation portions and the drive unit, wherein, after the alternating current voltage is applied to the pixel formation portions, the balance control unit controls the drive unit to sequentially activate the scanning signal lines in order to discharge the data voltage held in the pixel formation portions, and to bring a potential of the data signal lines to a reference voltage.

7. The liquid crystal display device according to claim 6 , wherein the off signal is a Display off Command configured to stop a function of the display unit of the liquid crystal display device, and the liquid crystal display device shifts to a display-off period after the data voltage written into the pixel formation portions is discharged.

8. The liquid crystal display device according to claim 6 , further comprising: a power supply circuit configured to supply a power supply voltage, wherein the off signal is a SLEEPIN Command configured to cause the liquid crystal display device to shift to a sleep period, and upon receiving the SLEEPIN Command, the balance control unit dives the power supply circuit to stop supplying the power supply voltage after discharging the data voltage written into the pixel formation portions.

9. The liquid crystal display device according to claim 1 , further comprising: data signal lines and scanning signal lines, both of which are configured to connect the pixel formation portions and the drive unit and are formed in the display unit, wherein each of the pixel formation portions includes: a pixel capacitance configured to hold the data voltage; and a switching element having a control terminal connected to the scanning signal line, a first conduction terminal connected to the data signal line, and a second conduction terminal connected to the pixel capacitance, and the switching element includes a thin film transistor having a channel layer formed of an oxide semiconductor.

10. The liquid crystal display device according to claim 9 , wherein the oxide semiconductor contains indium gallium zinc oxide.

11. The liquid crystal display device according to claim 1 , wherein a polarity of the alternating current voltage is reversed a plurality of times in one frame period.

12. The liquid crystal display device according to claim 1 , wherein a waveform of the alternating current voltage is rectangular.

13. The liquid crystal display device according to claim 1 , wherein an amplitude of the alternating current voltage is an amplitude of a voltage equal to or larger than a voltage value corresponding to a maximum brightness of an image represented by the input image data.

14. A method for driving a liquid crystal display device that applies a voltage corresponding to input image data to a liquid crystal layer of a display unit, and displays an image represented by the input image data on the display unit, the method comprising: a drive step of applying the voltage corresponding to the input image data to the liquid crystal layer; and a polarity bias reduction step of, upon receiving an off signal that issues an instruction to stop at least a part of functions of the liquid crystal display device, applying an alternating current voltage to the liquid crystal layer to reduce a polarity bias due to a voltage applied to the liquid crystal layer until a point of time when the off signal is inputted, wherein the display unit includes a plurality of pixel formation portions configured to hold, as a data voltage, the voltage to be applied to the liquid crystal layer, the method further comprising the steps of: obtaining a polarity bias value of the voltage applied to the liquid crystal layer, generating the alternating current voltage upon receiving the off signal, controlling the drive step so that applying of the voltage is different before and after a point of time when the off signal is inputted, and after the point of time when the off signal is inputted, when the polarity bias value at the point of time when the off signal is inputted is larger than “0”, the polarity bias value being obtained by the polarity bias calculation unit, the drive step applies, to each of the plurality of pixel formation portions, the alternating current voltage.